Tag: node

In my MEAN application I had a need to get the list of all open websockets during a particular request. Turns out with socket.io this is easily doable if can save a reference to the socketio variable during initialization.

For a typical socket.io init in Express, the app.js would contain the following code:

So what you need to do is save a reference to the “socketio” variable, which can be retrieved from the request passed down in Express, and used to get all sockets. To do so, you can set it as an application-wide variable in Express like so in app.js:

app.set('socketio', socketio);

Next, a typical Express function handling a request looks like so:

function(req, res) {
}

From your request (the “req” variable) you can get a reference to the Express app, which allows you to get a reference to the socketio variable you set application wide, which you can use to get the list of sockets. Like so:

Sometimes you need a list of all connected sockets in your server side API. This could be, for example, if you want to loop through all the sockets and emit something when a certain event happens, such as some a data model updating or something else.

As of socket.io version 1.3, you have access to all sockets using “socketio.sockets.sockets” programatically.

So for example if you needed all sockets in an Express controller running on node.js, you could access it this way.

In your server side app.js, socket.io is usually configured in express this way:

If you’ve ever scrolled through the Facebook newsfeed, you’ve noticed that the topmost stories are the most recent ones, and as you scroll to the bottom, older ones get loaded over and over as you keep scrolling.

This feature is firstly kind of “cool”, and fits in perfectly in a single page application. It’s also pretty useful from a performance standpoint, since not all of the documents (items your page is displaying, such as Facebook news stories, classified ads, search results, etc.) need to be loaded up front all at once when the user first lands on the page.

Paginating your documents in a MEAN application can be accomplished fairly easily, though it isn’t necessarily obvious. So I thought I’d write about the process I took, and the code I wrote, to get it done.

Let’s start with the AngularJS side of things. I used the ngInfiniteScroll module (https://github.com/sroze/ngInfiniteScroll) to accomplish the continuous scrolling effect. It’s pretty simple to configure, so please read up on the documentation. Essentially it can just be wrapped around an Angular ng-repeat directive, and be configured with a function to call to fetch more documents when the bottom of the page is reached (ngInfiniteScroll does all the calculations internally). Here is an example of what it would look like for getting more “classifieds” from the database to add them to the view:

So in the example above, the getMorePosted() function in your controller is called whenever ngInfiniteScroll detects that the user is at the bottom of the page. Note here that ngInfiniteScroll will most likely trigger right when the user lands on the page, unless you pre-load some documents in your controller. I elected getMorePosted() to fetch both the initial set of documents, and every successive set of documents as well. Depending on how you set things up, this may or may not make a difference, but it did for me.

My getMorePosted() function in the controller looks like this (note: it uses a factory called Classified to do the actual getting of classifieds from the API (Express/MongoDB on the server side of MEAN) which I’ll define later):

A couple things to note here. When the classifieds are being loaded, the $scope.loadingClassifieds flag is set to true. This disables ngInfiniteScroll from attempting to keep loading more classifieds when the bottom is reached, and it can also be used to put up a message to the user that loading is underway (in case it doesn’t happen near instantly due to a slow connection). Furthermore, getMorePosted() also tracks through the $scope.noMoreClassifieds flag when the end has reached (if ever, depending on how many thousands or millions of documents are in your database, and how far down the user scrolls). It does this by measuring the number of documents returned, and if the number equals zero, it means the end of pagination has been reached.

This is how getPosted() and getMorePosted() look like in the Classified factory:

So note that in my setup, the service loads and maintains the list of documents (postedClassifieds) within memory. And getPosted() returns that list if it is already loaded, and it also gets the first set of documents. getMorePosted() is where the magic happens. It gets the timestamp of the last classified, and transmits that to the API (server side, Express) which then loads the next “page” after for all documents (classifieds in this case) after that timestamp.

Before we continue to examine the server side, it’s important to note that you’ll need a field to sort by in a descending order (or ascending if you want you want the oldest documents up front). A timestamp value will work great. Otherwise a MongoDB ID could work too, since those are incremental. It will depend on your data. In my case, a timestamp called “posted” was available in my data, and very consistent. Documents could only be removed from before a past timestamp, but not added to in a past timestamp (even then, this wouldn’t be a huge problem). So that works just fine with this pagination approach.

Note that “Classified” defines my model, which is queried from using Mongoose. I limit the number of documents returned to 20, which works well for my application. And the query is sorted in descending order by the “posted” field, which is a timestamp. You’ll notice a where clause added, which gets only the classifieds posted before the time sent in (“startTime”) from the UI, so that works in conjunction with the sort and returns 20 more classifieds before the “startTime”. Also note that I send the timestamp in milliseconds, which gives a nice clean number that can be sent down to the API from the UI.

And, that’s it!

Something I want to add is that on your client side (in AngularJS) if you end up loading too many documents/items in your ng-repeat, the application performance will greatly degrade. With ngInfiniteScroll, all items on the page are always kept once they’re loaded, even if they’re not in the view currently. There’s another module: https://github.com/angular-ui/ui-scroll which will allow you to destroy and re-create items as they go in and out of the view from the user’s browser as the user scrolls through. This will vastly improve performance when a lot of documents are loaded.

For the MEAN application I’m currently building, there is a requirement to have it served in multiple user-selectable languages. I used the MEAN fullstack generator (https://github.com/DaftMonk/generator-angular-fullstack), which does not provide i18n (internationalization) support.

When setting up my application for i18n, I realized that I needed translations available up and down the stack. So not just in the View, also in the Model and Controller. I ended up using angular-translate (https://github.com/angular-translate/angular-translate) and MomentJS (https://github.com/moment/moment/) in the client side AngularJS. And I created my own custom solution, very simple, in Node for the server side model and controller.

I think angular-translate works great in Angular, and there are plenty of guides around so I won’t go into it. But I want to mention that angular-translate doesn’t have great support (at least that I could find) for translating dates and numbers. This is where MomentJS can fill in the gaps. Again, plenty of guides out and good documentation out there for MomentJS.

For Node, I created a module that simply has a JSON of all the translations, and a function that returns the translation. Example below: